1. Technical Field
The present invention relates to an electronic ink display device and a driving method. More particularly, the present invention relates to an electronic ink display device capable of displaying colors without a color filter and a method for driving the same.
2. Related Art
Cathode ray tubes are used as a monitor of a measurement instrument and an information terminal device such as a TV. Due to weight and size, cathode ray tubes are replaced with flat panel display devices such as an Liquid Crystal Display (“LCD”) device, a Plasma Display Panel (“PDP”), and an Electro Luminescent Display (“ELD”), an electronic ink display device.
Electronic ink display devices called “a DPD (Digital Paper Display) device” may be manufactured at a low cost and need lower energy. Electronic ink display devices may have no separate backlight unit and have a wide viewing angle. Electronic ink display devices may be bent repeatedly and preserve resolution and contrast despite repetitive bending. Electronic ink display devices may be for use with a portable computer, an electronic newspaper, a smart card, etc. Electronic ink display devices may replace traditional print media such as books, newspapers, and magazines.
Electronic ink used in electronic ink display devices includes particles. The particles are floatably included in a capsulated fluid. The particles have a negative or positive charge so that phoresis can be performed to the particles. Accordingly, electronic ink display devices display an image by applying electric fields to the electronic ink and regulating the phoresis of the particles in the electronic ink.
FIG. 1 is a cross-sectional view illustrating an electronic ink display device which uses an electronic ink panel 100. The electronic ink panel 100 includes first and second substrates 2 and 4 facing each other. A middle electronic ink layer 10 is interposed between the first and second substrates 2 and 4.
Gate electrodes 3 and gate wires (not shown) are formed on the second substrate 4. The gate wires are electrically connected to the gate electrodes 3. A gate insulation layer 5 is formed on the second substrate 4 having the gate electrodes 3 and the gate wires. Channel layer patterns 7 are formed at portions corresponding to the gate electrodes 3 on the gate insulation layer 5. The channel layer patterns 7 are formed by disposing a semiconductor material layer on the gate insulation layer 5 and patterning the semiconductor material layer. Source and drain electrodes 9A and 9B are separated from each other and formed on the surface of each channel layer pattern 7. Data wires (not shown) are formed together with the source and drain electrodes 9A and 9B. The data wire is electrically connected to the source electrode 9A. A protection layer 11 having contact holes is formed on and above the entire surface of the second substrate 4. The source and drain electrodes 9A and 9B are formed. Each of the contact holes exposes a portion of the surface of the corresponding drain electrode 9B. Second electrode patterns 8 are electrically connected to the drain electrodes 9B and are formed on the protection layer 11. Each of the second electrode patterns 8 is located in a sub-pixel region divided by the gate wires and the data wires.
A black matrix is formed on the first substrate 2. The surface of the first substrate 2 is divided into a plurality of sub-pixel regions by the black matrix 19. A color filter 18 is formed on the surface of the first substrate 2 which is exposed through the black matrix 19. The color filter 18 includes sub-color filters 18A, 18B, and 18C of red, green, and blue. A first electrode 6 is formed on the surfaces of the sub-color filters 18 and the black matrix 19.
The first and second substrate 2 and 4 are disposed on both surfaces of the electronic ink layer 10 so that the first electrode 6 and the second electrode patterns 8 face each other. In other words, the electronic ink layer 10 is located between the first electrode 6 and the second electrode patterns 8. The electronic ink layer 10 includes a binder film 12 in which a micro-capsulated ink capsule 14 is dispersed and contained. The binder film 12 is formed of a polymer. The ink capsule has a diameter of approximately a few hundred micrometers. The ink capsule 14 includes a fluid 16 which is filled with one of an organic material and an inorganic material. At least one kind of electrified particles 20 is injected into the fluid of the ink capsule 14. Phoresis is performed with respect to the particles in response to an electric field applied between the first electrode 6 and the second electrode pattern 8. A color image may be displayed on the first substrate 2 in which the color filter 18 is formed.
The particles 20 include white first particles 22 of a positive charge and black second particles 24 of a negative charge. Phoresis is performed with respect to the first and second particles 22 and 24 according to the electric fields between the first electrode 6 and the second electrode patterns 8. An image corresponding to the gradation of white and black colors may be displayed on the electronic ink layer 10. As the black and white image on the electronic ink layer 10 is projected to the first substrate 2 having the color filter 18, a color image appears on the electronic ink panel (i.e. the first substrate 2).
FIGS. 2A to 2C show the phoresis state of the first and second particles 22 and 24 of FIG. 1 according to electric fields. FIG. 2A shows that upon application of a voltage −V of the negative polarity to the first electrode 6 and a voltage +V of the positive polarity to the second electrode pattern 8, the white first particles 22 of a positive charge are concentrated to the first electrode 6. At the same time, the black second particles 24 of a negative charge are concentrated to the second electrode 8. The difference between the voltage −V of the negative polarity and the voltage +V of the positive polarity is set large enough to perform phoresis with respect to the first and second particles 22 and 24. Due to the white color of the first particles 22 concentrated to the first electrode 6, a large amount of light from outside is reflected toward the color filter 18. Sub-pixels of red, green, and blue of the highest gradation are displayed on the first substrate 2 according to the sub-color filters 18A, 18B, and 18C.
In FIG. 2B, upon application of a voltage +V of the positive polarity to the first electrode 6 and a voltage −V of the negative polarity to the second electrode pattern 8, the white first particles 22 of a positive charge are concentrated to the second electrode 8 and the black second particles 24 of a negative charge are concentrated to the first electrode 6. The black color of the second particles 24 concentrated to the first electrode 6 may absorb almost all the light from outside. Therefore, sub-pixels of red, green, and blue of the lowest gradation are displayed on the first substrate 2 according to the sub-color filters 18A, 18B, and 18C.
FIG. 2C shows that voltages +V of the positive polarity, voltages −V of the negative polarity or voltages of very small voltage differences are applied to all of the first electrode 6 and the second electrode pattern 8. In this case, the first and second particles 22 and 24 are concentrated to a central portion between the first electrode 6 and the second electrode pattern 8 by the attractive force. About a half of the light from outside is reflected toward the color filter 18 by the white color of the first particles 22 and the black color of the second particles 24. Therefore, sub-pixels of red, green, and blue which have a middle gradation are displayed on the first substrate 2 according to the sub-color filters 18A, 18B, and 18C.
As mentioned above, the related art electronic ink panel includes the color filter 18 to display a color image. The color filter 18 reflects some of the light to be transmitted and may deteriorate the optical efficiency of the electronic ink panel. The color filter may increase the thickness of the electronic ink panel and complicate the manufacturing process of the electronic ink panel. Accordingly, there is a need of an electronic ink panel that overcomes drawbacks of the related art panel.